Tag Archives: Human

The cover story of the July Scientific American is on brain physics. It persuades me that raw brain hardware was more important than I’d thought in our history. Here is my current best guess on brain history.

Across diverse species we see strong convergence in brain organization, especially conditional on brain size. Species differ more in their brain hardware components, and their energy sources. For example, primates have innovative cell designs allowing higher neuron density. Given access to such cells, primates could afford to evolve bigger brains, and then bigger pair-bond-based social groups.

Humans found a way to use big primate brains to support big-group far-traveling long-life versions which could access richer energy sources, which in turn supported large energy-hungry brains. Humans found a way to use those huge old social brains to support robust accumulation of culture, which is our main advantage over other primates. This was probably supported by only minor changes in brain organization.

While the brains of smarter humans today may use a better set of long term connections, probably most of their advantage comes from using more energy-intensive brain hardware. So it probably wasn’t until our recent cheap energy era that high IQ humans gained large advantages. The tendency 0f smarter humans to choose lower fertility lowers their advantage today.

I hadn’t till now appreciated how central long distance travel was to early human evolution. A 2004 Naturearticle:

No primates other than humans are capable of endurance running. … Well-conditioned human runners … can occasionally outrun horses over the extremely long distances that constrain these animals to optimal galloping speeds, typically a canter. … Horses have … narrow ranges of preferred speeds for trotting and galloping and gait transitions that minimize cost. … Human runners differ from horses in employing a single gait. … Humans are thus able to adjust running speed continuously without change of gait or metabolic penalty over a wide range of speeds. …

Considering all the evidence together, it is reasonable to hypothesize that Homo evolved to travel long distances by both walking and running… Endurance running is not common among modern hunter-gatherers, who employ many technologies to hunt (for example, bows and arrows, nets and spearthrowers), thereby minimizing the need to run long distances. But Carrier has hypothesized that endurance running evolved in early hominids for predator pursuit before these inventions in the Upper Palaeolithic (about 40kya). Endurance running may have helped hunters get close enough to throw projectiles, or perhaps even to run some mammals to exhaustion in the heat. …

Another hypothesis to explore is … in the open, semi-arid environments … early Homo may … have needed to run long distances to compete with other scavengers, including other hominids. … Similar strategies of ‘pirating’ meat from carnivores are sometimes practised by the Hadza in East Africa. … It is known that major increases in encephalization occurred only after the appearance of early Homo. … Endurance running may have made possible a diet rich in fats and proteins thought to account for the unique human combination of large bodies, small guts, big brains and small teeth.

A 2009 Evolutionary Anthropologyarticle on “The Emergence of Human Uniqueness”

Important preadaptations in the genus Homo … led to human uniqueness. First, hominins are bipedal and, as a result, cover geographical ranges far larger than other apes do. Even hunter-gatherers living in tropical forests have daily home ranges that are two to three times those of chimpanzees, and lifetime home ranges more than two orders of magnitude greater. Thus, individual hominins faced more environmental variability than do chimpanzees. … This would favor social learning capacity.

Second, bipedal hominins evolved exceptional manual dexterity because their hands were freed from locomotory constraints, and they could carry tools with little cost. This would have favored increased tool using and making behavior and probably increased selection pressure on imitative capacities as well. Third, by at least 2 million years ago, hominins had begun to depend on high-quality, widely dispersed resources that were difficult to obtain. This shift of feeding niche had important life-history implications. Juveniles could not fully feed themselves due to the complexity of the extractive niche, and this led to their provisioning by close kin. As large package foods became common, the foods returned to the juvenile home base were probably ‘‘shared’’ by coresidents. This …. might partially explain why hunter-gatherers experience early adult mortality at one-ﬁfth the rate of wild chimpanzees. That pattern would favor a life history with later age at maturity and delayed onset of senescence. … Continue reading "Travel Made Humans" »

Why do we have ginormous brains? Animals tend to have big brains when they have big bodies, but beyond that the main brain patternissocial: bigger brains are found in birds and mammals that compete with predators or prey, and who manage pair-bonding mate relations. The extra costs of big brains is outweighed by benefits of not being out-witted by others.

Primates (and hyenas) hit on the trick of reusing pair-bonding skills to manage friendships in large social groups. Primates have huge expensive brains, which are bigger in species with larger social groups, and these groups spend more of their time managing social relations. Bigger groups better protect against predators, though the coalition politics of dominance gets more complex in bigger groups.

Primates not only manage relations and coalitions, but they also track the relations and coalitions of others. They are adept at judging how to help their coalitions, and when to switch sides. The top chimp is often not the strongest, but instead the one with the strongest coalition, which gets to dominate food and mating, and stay best protected from predators; chimp investments in big brains often pay off handsomely.

Humans have the biggest primate brains of all. Over the last two million years hominid brains grew more where climates were variable, but they grew most where population densities were high. This suggests that human brains were also big mainly due to social pressures. The “mating mind” sexual selection hypothesis seems at odds with this density effect, and with the more general fact that polygamous species tend to have smaller brains. “Man the tool user” stories seem to confuse broad group gains with individual benefits – smaller brains seem sufficient for copying others’ tool skills. But even if social pressures were key, which pressures exactly?

Isolated nomadic forager bands today are “fossils” with crucial clues about our distant ancestors. Anthropologists who study them reportthat overt dominance is rare, and long distances make war rare (as 4 million year old fossils suggest). Foragers live in tight quarters and use language to express and enforce social norms on food sharing, non-violence, mating freedom, communal decision making, and norm enforcement. Anger, bragging, giving orders, and anything remotely resembling dominance among men is punished by avoidance, exile, and death as required. Human’s unusual hidden female fertility also limits male dominance temptations.

The puzzle here is that consistent enforcement of such norms seems to drastically reduce the payoff to expensive coalition-politics-savvy brains. If you can’t collude to grab the food or the women, and everyone is treated fairly based on their contributions, why bother to be so clever? Yes, some brain innovations were required to support language, and maybe they wouldn’t have occurred in a small brain, but after that innovation human brains could have shrunk (as perhaps with hobbits). Why did humans keep huge expensive brains?

In a messy real world, social norms expressed in language typically have many iffy boundary cases and ambiguities. How much of what sort of food of what quality offered how conveniently counts as food sharing? How big a frown is a grimace? Sex with how close a relative counts as incest? And so on. This wouldn’t matter if boundary cases were decided randomly, but that seems unlikely. Instead big brain gains come five ways:

Unnormed – coalition politics on acts uncovered by norms.Skirt – keep actions near but not over edge of violating norms.Cover – politics of observers on if to report an act to others.Frame – lawyer-like arguing on if acts violate social norms.Conspire – form coalitions on how to publicly interpet iffy acts.

Most norms have meta-norms against consciously trying to evade them. Self-deception should help here; foragers might sincerely believe they usually just do their job and “tell it like it is”, and then unconsciously try to act, selectively report and frame acts, and support interpretation coalitions, to their advantage. Instead of “man the tool user”, we might be better understood as “man the sly rule bender.”

Gains to rule bending could be greatly reduced via social norms with very clear simple rules. But humans seems to usually prefer complex and ambiguous rules that require “judgment” to apply. For example, foragers often have complex incest rules, forbidding a much wider range of sex partners than is needed to prevent genetic problems. And acts of sorcery are allowed to count as acts of aggression that violate social norms and must be punished, even without concrete evidence showing such acts. Both complex broad incest rules and allowing sorcery complaints greatly increase the scope for gains to large rule-bending brains, and suggest that we tend to prefer to allow such scope.

The idea that the main reason we have huge brains is to hypocritically bend rules seems to me a dramatic change in how we think about human nature. If true, it should change how we understand a great many things in psychology and social science. I’ve been obsessing about his topic for weeks, and last Thursday I ran it past Robin Dunbar, famed for his contributions to the social brain account, and he said it was pretty close to his view on the subject, and he suggested the incest example.